1. Technical Field of the Invention
The present invention relates generally to high performance structural resins for advanced aerospace applications. It relates particularly to a tough, solvent resistant, crystalline imide/arylene block copolymer with a broad melting point, and especially to adhesives and composites thereof.
2. Description of the Prior Art
Polyimides are condensation polymers commonly synthesized by the reaction of aromatic dianhydrides with aromatic diamines. The intermediate poly(amic acid) is either thermally or chemically cyclodehydrated to form the polyimide, which has a repeat unit of the general type ##STR1## Ar is a tetravalent aromatic radical which can be as simple as 1,2,4,5-tetrasubstituted benzene, or may be as complex as a bis-4-(o-diphenylene) having the general structure ##STR2## where X=nil, O, S, SO.sub.2, C.dbd.O, etc. As well, Ar may be any other appropriate tetravalent radical. Ar' is a divalent aromatic radical which may be 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 4,4'-oxydiphenylene, 4,4'-thiodiphenylene, 4,4'-carbonyldiphenylene, 4,4'-methanediphenylene or any other appropriate divalent radical.
Synthesis and characterization of polyimides has been extensively reported in the literature. The preparation of aromatic polyimides by reaction of an aromatic dianhydride with an aromatic diamine, followed by thermal cyclization was first reported in 1963 [G. M. Bower and L. W. Frost, Journal of Polymer Science A1, 3134 (1963)] with patents awarded in 1965 [Edwards, U.S. Pat. No. 3,179,614 and U.S. Pat. No. 3,179,634; Endrey, U.S. Pat. No. 3,179,631 and U.S. Pat. No. 3,179,633]. Several reviews on polyimides have been published [S. E. Sroog, "Polyimides" in Encyclopedia of Polymer Science and Technology, (H. F. Mark, N. G. Gaylord, and N. M. Bikales, Ed.), Interscience Publishers, New York, 1969 Vol. 11, pp. 247-272; N. A. Adrova, M. I. Bessonov, L. A. Lauis and A. P. Rudakov, Polyimides, Technomic Publishing Co., Inc., Stamford, Conn., 1970].
Wholly aromatic polyimides are known for their exceptional thermal, thermooxidative, and chemical resistance but are generally difficult to process as structural adhesives or composite matrices. Several polymides such as Kapton.RTM. [DuPont], PI-2080 [Upjohn], XU-218 [Ciba-Geigy], Ultem.RTM. [General Electric], and LARC-TPI [Mitsui Toatsu] are commonly available commercially and used as films, moldings, adhesives, and composite matrices.
Poly(arylene ethers) are condensation polymers commonly synthesized by nucleophilic displacement of activated aromatic halides in polar solvents by alkali metal phenates to form a repeat unit of the general type ##STR3## Ar is arylene and y=C.dbd.O, SO.sub.2, etc. ##STR4## Nucleophilic displacement reactions leading to high molecular weight poly(arylene ethers) were initially reported in 1958 [A. Kreuchumas, U.S. Pat. No. 2,822,351 (1958)]. Since then, numerous papers [R. N. Johnson, et al., J. Polym. Sci. A1, 5,2375 (1967); S. V. Vinogradova, et al., Polym. Sci. USSR, 14, 2963 (1972); J. B. Rose, Polymer, 15, 456 (1974); T. E. Attwood, et al., Polym. Prepr., 20(1), 191 (1979); R. Viswanathan, et al., Polymer, 25, 1927 (1984); and P. M. Hergenrother, et al., Polymer, 29, 258 (1988)] and patents [Jones, British 1,016,245 (1962), Vogel, British 1,060,546 (1963); Goodman, et al., British 971,277 (1964); Farnham, et al., British 1,078,234 (1973); and Farnham U.S. Pat. No. 4,175,175 (1979)] have appeared.
Poly(arylene ethers) are known for their good mechanical properties, good thermooxidative stability, relative ease of processing, and solubility in common organic solvents. For certain applications, resistance to common organic solvents is a requirement. Several poly(arylene ethers) such as Udel.RTM. polysulfone [Amoco], Kadel.RTM. polyketone [Amoco], PEEK.RTM. polyetherketone [ICI] are commercially available and used as films, moldings, adhesives, and composite matrices.
Amine terminated arylene ethers have been prepared by several different methods. The preparation of amine terminated polysulfone oligomers using p-aminophenol as the end-capping compound was reported in 1974 [J. H. Kawakami, et. al., J. Polym. Sci. Poly. Chem. Ed., 12, 565 (1974)]. More recently, the preparation of amine terminated polysulfone and poly(arylene ether ketone) oligomers using m-aminophenyl-4'-hydroxyphenyl-2.2-isopropylidene has been reported [M. J. Jurek, et al., Polym. Prepr., 26(2), 283 (1985); G. D. Lyle, et al., Polym. Prepr., 28(1) 77 (1987)].
The introduction of crystallinity into a polymer has long been recognized as an effective means of improving the solvent resistance and increasing the modulus. In addition, if the proper degree and type of crystallinity is attained, the material can also display extremely high toughness. Notable examples are PEEk.RTM. polyetheretherketone [IC] and LARC-CPI [P. M. Hergenrother, et al., SAMPE Journal., 24(4) 13 (1988)] which exhibit very high fracture toughness (G.sub.IC, critical strain energy release rate) and are highly solvent resistant.